From: Alexander Aring <alex.aring@gmail.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Stefan Schmidt <stefan@datenfreihafen.org>,
linux-wpan - ML <linux-wpan@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
"open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
Michael Hennerich <michael.hennerich@analog.com>,
Harry Morris <h.morris@cascoda.com>,
Varka Bhadram <varkabhadram@gmail.com>,
Xue Liu <liuxuenetmail@gmail.com>, Alan Ott <alan@signal11.us>,
David Girault <david.girault@qorvo.com>,
Romuald Despres <romuald.despres@qorvo.com>,
Frederic Blain <frederic.blain@qorvo.com>,
Nicolas Schodet <nico@ni.fr.eu.org>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
"linux-wireless@vger.kernel.org Wireless"
<linux-wireless@vger.kernel.org>
Subject: Re: [wpan-next v2 18/27] net: mac802154: Handle scan requests
Date: Sun, 16 Jan 2022 17:44:18 -0500 [thread overview]
Message-ID: <CAB_54W5xJV-3fxOUyvdxBBfUZWYx7JU=BDVhTHFcjJ7SOEdeUw@mail.gmail.com> (raw)
In-Reply-To: <20220114194425.3df06391@xps13>
Hi,
On Fri, 14 Jan 2022 at 13:44, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Alexander,
>
> alex.aring@gmail.com wrote on Thu, 13 Jan 2022 19:01:56 -0500:
>
> > Hi,
> >
> > On Thu, 13 Jan 2022 at 12:07, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> > >
> > > Hi Alexander,
> > >
> > > alex.aring@gmail.com wrote on Wed, 12 Jan 2022 17:44:02 -0500:
> > >
> > > > Hi,
> > > >
> > > > On Wed, 12 Jan 2022 at 12:33, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> > > > ...
> > > > > + return 0;
> > > > > +}
> > > > > diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c
> > > > > index c829e4a75325..40656728c624 100644
> > > > > --- a/net/mac802154/tx.c
> > > > > +++ b/net/mac802154/tx.c
> > > > > @@ -54,6 +54,9 @@ ieee802154_tx(struct ieee802154_local *local, struct sk_buff *skb)
> > > > > struct net_device *dev = skb->dev;
> > > > > int ret;
> > > > >
> > > > > + if (unlikely(mac802154_scan_is_ongoing(local)))
> > > > > + return NETDEV_TX_BUSY;
> > > > > +
> > > >
> > > > Please look into the functions "ieee802154_wake_queue()" and
> > > > "ieee802154_stop_queue()" which prevent this function from being
> > > > called. Call stop before starting scanning and wake after scanning is
> > > > done or stopped.
> > >
> > > Mmmh all this is already done, isn't it?
> > > - mac802154_trigger_scan_locked() stops the queue before setting the
> > > promiscuous mode
> > > - mac802154_end_of_scan() wakes the queue after resetting the
> > > promiscuous mode to its original state
> > >
> > > Should I drop the check which stands for an extra precaution?
> > >
> >
> > no, I think then it should be a WARN_ON() more without any return
> > (hopefully it will survive). This case should never happen otherwise
> > we have a bug that we wake the queue when we "took control about
> > transmissions" only.
> > Change the name, I think it will be in future not only scan related.
> > Maybe "mac802154_queue_stopped()". Everything which is queued from
> > socket/upperlayer(6lowpan) goes this way.
>
> Got it.
>
> I've changed the name of the helper, and used an atomic variable there
> to follow the count.
>
> > > But overall I think I don't understand well this part. What is
> > > a bit foggy to me is why the (async) tx implementation does:
> > >
> > > *Core* *Driver*
> > >
> > > stop_queue()
> > > drv_async_xmit() -------
> > > \------> do something
> > > ------- calls ieee802154_xmit_complete()
> > > wakeup_queue() <--------/
> > >
> > > So we actually disable the queue for transmitting. Why??
> > >
> >
> > Because all transceivers have either _one_ transmit framebuffer or one
> > framebuffer for transmit and receive one time. We need to report to
> > stop giving us more skb's while we are busy with one to transmit.
> > This all will/must be changed in future if there is hardware outside
> > which is more powerful and the driver needs to control the flow here.
> >
> > That ieee802154_xmit_complete() calls wakeup_queue need to be
> > forbidden when we are in "synchronous transmit mode"/the queue is
> > stopped. The synchronous transmit mode is not for any hotpath, it's
> > for MLME and I think we also need a per phy lock to avoid multiple
> > synchronous transmissions at one time. Please note that I don't think
> > here only about scan operation, also for other possible MLME-ops.
> >
>
> First, thank you very much for all your guidance and reviews, I think I
> have a much clearer understanding now.
>
> I've tried to follow your advices, creating:
> - a way of tracking ongoing transmissions
> - a synchronous API for MLME transfers
>
Please note that I think we cannot use netif_stop_queue() from context
outside of netif xmit() callback. It's because the atomic counter
itself is racy in xmit(), we need to be sure xmit() can't occur while
stopping the queue. I think maybe "netif_tx_disable()" is the right
call to stop from another context, because it holds the tx_lock, which
I believe is held while xmit().
Where the wake queue call should be fine to call..., maybe we can
remove some EXPORT_SYMBOL() then?
I saw that some drivers call "ieee802154_wake_queue()" in error cases,
may we introduce a new helper "?ieee802154_xmit_error?" for error
cases so you can also catch error cases in your sync tx. See `grep -r
"ieee802154_wake_queue" drivers/net/ieee802154`, if we have more
information we might add more meaning into the error cases (e.g.
proper errno).
> I've decided to use the wait_queue + atomic combo which looks nice.
> Everything seems to work, I just need a bit of time to clean and rework
> a bit the series before sending a v3.
>
Okay, sounds good to implement both requirements.
- Alex
next prev parent reply other threads:[~2022-01-16 22:44 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-12 17:32 [wpan-next v2 00/27] IEEE 802.15.4 scan support Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 01/27] net: mac802154: Split the set channel hook implementation Miquel Raynal
2022-01-12 22:30 ` Alexander Aring
2022-01-12 22:53 ` Alexander Aring
2022-01-13 11:12 ` Miquel Raynal
2022-01-13 9:32 ` Miquel Raynal
2022-01-13 23:27 ` Alexander Aring
2022-01-12 17:32 ` [wpan-next v2 02/27] net: mac802154: Ensure proper channel selection at probe time Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 03/27] net: ieee802154: Improve the way supported channels are declared Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 04/27] net: ieee802154: Give more details to the core about the channel configurations Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 05/27] net: mac802154: Convert the symbol duration into nanoseconds Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 06/27] net: mac802154: Set the symbol duration automatically Miquel Raynal
2022-01-12 22:25 ` Alexander Aring
2022-01-13 9:52 ` Miquel Raynal
2022-01-13 23:36 ` Alexander Aring
2022-01-14 10:18 ` Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 07/27] net: ieee802154: hwsim: Ensure frame checksum are valid Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 08/27] net: ieee802154: Drop symbol duration settings when the core does it already Miquel Raynal
2022-01-12 22:26 ` Alexander Aring
2022-01-13 11:16 ` Miquel Raynal
2022-01-13 23:34 ` Alexander Aring
2022-01-14 10:21 ` Miquel Raynal
2022-01-16 23:21 ` Alexander Aring
2022-01-17 9:12 ` Miquel Raynal
2022-01-17 23:38 ` Alexander Aring
2022-01-18 10:38 ` Miquel Raynal
2022-01-18 22:43 ` Alexander Aring
2022-01-19 22:26 ` Miquel Raynal
2022-01-19 23:26 ` Alexander Aring
2022-01-12 17:32 ` [wpan-next v2 09/27] net: ieee802154: Move IEEE 802.15.4 Kconfig main entry Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 10/27] net: mac802154: Include the softMAC stack inside the IEEE 802.15.4 menu Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 11/27] net: ieee802154: Move the address structure earlier Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 12/27] net: ieee802154: Add a kernel doc header to the ieee802154_addr structure Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 13/27] net: ieee802154: Return meaningful error codes from the netlink helpers Miquel Raynal
2022-01-12 17:32 ` [wpan-next v2 14/27] net: ieee802154: Add support for internal PAN management Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 15/27] net: ieee802154: Define a beacon frame header Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 16/27] net: ieee802154: Define frame types Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 17/27] net: ieee802154: Add support for scanning requests Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 18/27] net: mac802154: Handle scan requests Miquel Raynal
2022-01-12 22:44 ` Alexander Aring
2022-01-13 17:07 ` Miquel Raynal
2022-01-14 0:01 ` Alexander Aring
2022-01-14 18:44 ` Miquel Raynal
2022-01-16 22:44 ` Alexander Aring [this message]
2022-01-16 22:50 ` Alexander Aring
2022-01-17 9:00 ` Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 19/27] net: ieee802154: Full PAN management Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 20/27] net: ieee802154: Add support for beacon requests Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 21/27] net: mac802154: Handle beacons requests Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 22/27] net: ieee802154: Trace the registration of new PANs Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 23/27] net: mac802154: Add support for active scans Miquel Raynal
2022-01-12 23:16 ` Alexander Aring
2022-01-13 17:14 ` Miquel Raynal
2022-01-14 0:30 ` Alexander Aring
2022-01-14 0:39 ` Alexander Aring
2022-01-12 17:33 ` [wpan-next v2 24/27] net: mac802154: Add support for processing beacon requests Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 25/27] net: mac802154: Inform device drivers about scans Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 26/27] net: mac802154: Inform device drivers about beacon operations Miquel Raynal
2022-01-12 17:33 ` [wpan-next v2 27/27] net: ieee802154: ca8210: Refuse most of the scan operations Miquel Raynal
2022-01-12 22:48 ` Alexander Aring
2022-01-13 9:29 ` Miquel Raynal
2022-01-14 1:00 ` Alexander Aring
2022-01-14 18:37 ` Miquel Raynal
2022-01-16 22:48 ` Alexander Aring
2022-01-17 9:04 ` Miquel Raynal
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